1. Field of the Invention
This invention relates to a pipe structure in which an inner pipe is resiliently supported within an outer pipe, and, more particularly, to an improved structure for protecting an inner pipe before, during, and after installation.
2. Background Information
In various applications, composite pipe structures, made up of layers of different materials, have been used to combine the advantages of different materials in providing mechanical strength, resistance to corrosion, thermal insulation, and the like. For example, underground steel pipes have been wrapped or otherwise surrounded by non-metallic materials to prevent the corrosive effects of ground water. Oil well casings, which are formed by strings of steel pipes fastened together and lowered as the well is drilled, are typically protected by cement introduced into the annular space between the outside of the outer wall of the casing and the well bore, to prevent the migration of ground water into the well. In the petroleum industry, concrete inner liners have also been used within pipes handling corrosive liquids, such as oil field brines.
In the construction industry various types of insulation have been wrapped around metal pipes carrying hot and cold fluids, including chilled water lines, hot water lines, and coolant lines in air conditioning systems. Extruded cylinders made from elastomeric resin foams are now widely used in this way.
In the food processing and food transportation industries, glass vessels and glass lined vessels are used extensively, because glass surfaces are chemically inert in such applications. In addition, glass surfaces are preferred because glass does not contain toxic materials which can be leached into food products and because glass can be easily cleaned. Glass containers of well known types are commonly used for the storage and shipment of various types of liquid food products, and glass linings have been used with very large containers, such as, tank trucks for carrying milk or storage tanks for storing milk. The use of glass in such applications avoids corrosive processes known to occur when metallic surfaces are exposed to the weak acids present in many food substances. Such corrosive processes in a unlined metal vessel may result in the release of poisonous by products of corrosion into the food products, in the formation of corroded surfaces of the vessel which cannot be adequately cleaned, and in the ultimate destruction of a vessel.
The alternative use of resinous materials, or plastics, in food processing and transportation has been limited in certain instances by the fact that certain plastic materials may contain dangerous substances which can be leached into the food, and by the fact that, above certain temperatures, such materials may break down to release dangerous substances. Because they are inert to attack from almost all chemical substances, glass vessels and glass lined metal vessels have found practical use in a number of applications in the chemical processing and transportation industries, as well.
While the use of glass piping in food and chemical processing applications offers many advantages, tubular glass is rarely used for anything other than small structures because the brittleness of glass makes large tubes hard to handle and to install, and because a simple method for joining sections of relatively large glass pipe has not been found. Before the many advantages of glass lined piping can be widely used, solutions to the above problems must be found.